A standard press of the type used in the continuous production of fiberboard, particleboard, and the like has a rigid press frame having vertically spaced upper and lower parts defining a press gap that can extend some 30 m. Upper and lower belts are spanned in the respective press parts between respective upstream and downstream rollers, at least one of which is driven to advance confronting upper and lower stretches of the lower and upper belts longitudinally through the press. Upper and lower press plates bear, typically by some sort of roller arrangement, on the lower and upper surfaces of the upper and lower stretches of the lower and upper belts. The lower press plate is fixed The upper plate is vertically movable by means of a double-acting hydraulic actuator system.
The press plates can each be formed of one or more pieces. The rollers can be rods as described in U.S. Pat. No. 4,613,293 or cylindrical rollers formed together to a chain as described in U.S. Pat. No. 3,881,852. The pressure characteristic of the press, that is the amount of force exerted at different regions along the length of the press, is determined by the hydraulic actuators and itself determines the characteristics of the finished board. Coupled with the pressure characteristic is the temperature characteristic, as the temperature distribution of the platens can also vary. Both of these characteristics depend also from the throughput speed of the mat or laminate workpiece being pressed. All of these factors must be controlled to produce a high-quality product.
U.S. Pat. No. 4,645,632 describes a system wherein the lower press plate is supported via insulation on a rigid press table. The upper press plate is carried on at least one longitudinally extending beam which in turn is connected via the hydraulic actuators to the press frames. In order to set the press characteristic it is necessary to elastically deform the upper press plate and the beams, a ]ob that takes a considerable amount of force. At best it is impossible to deform the upstream ends of the platens sufficiently, that is to a small enough radius, to form the desired flared inlet mouth for the press.